One man's relentless search for his missing son led him to uncover one of the most shocking crimes in post-war Italy - a tale of satanism and violence that has gripped the country for more than a year.

Michele Tollis spent six years searching for his son Fabio

In January 1998 Fabio Tollis and Chiara Marino, both just 16, disappeared.

They had been drinking at a pub called the Midnight - the centre of the heavy metal scene in Milan - and they never came home.

The police and many of their friends just thought they had run off together. But their parents refused to accept this.

Michele Tollis, Fabio's father, began to attend metal concerts and festivals across Europe, handing out leaflets and quizzing Fabio's friends.

Fabio and his friends were into the most extreme forms of heavy metal music - death metal and black metal, music obsessed with images of murder and satanism - and the role of this music is central to the story.

No one can contradict me when I say that heavy metal and satanism are closely linked

Michele Tollis

It emerged that Chiara, the girl who disappeared with Fabio, had a collection of satanic literature and paraphernalia in her bedroom.

During this search, Michele Tollis became convinced that satanism had something to do with his son's disappearance.

"No one can contradict me when I say that heavy metal and satanism are closely linked. They're inseparable," he says.

Many of Fabio's friends appeared to be evasive when questioned about his whereabouts and Michele became convinced they were hiding something.

Over the next six years he built up a dossier of intelligence about them; who knew whom and which bands they played in.

'Alarm bells'

Then in January 2004 Michele was watching the local news. An item came on reporting a brutal murder in their nearby town of Somma Lombardo.

A young man called Andrea Volpe had been arrested and admitted killing his ex-girlfriend.

Fabio (c) and Chiara (second r) were members of Beasts of Satan

Alarm bells went off in Michele's head because Volpe had played in a death metal band with his son. He called the police and arranged a meeting.

"It was a strange story, the one Michele Tollis told," says Teniente Enzo Molinari of the carabinieri.

"But he didn't only tell a story; he backed it up with a very convincing body of paperwork and photographs which he had gathered over the past six years.

"He had carried out a true investigation on the disappearance of his son and his son's girlfriend, all on his own."

Using Michele's dossier of information, the police interrogated Volpe about the disappearances.

Beasts of Satan

Finally Volpe confessed and led the police to where Fabio and Chiara were buried.

If music makes itself an instrument of nefarious deeds and death it should be stopped

Don Aldo Buonaito, priest

Michele's hunt was over, but the revelations were just beginning.

One of Fabio's school friends, Mario Maccione, confessed to having beaten Fabio to death with a hammer.

He also revealed that the boys had been part of a wider satanic sect called the Beasts of Satan.

It was revealed Andrea Bontade, a drummer, had been terrorised into committing suicide.

Soon, other mysterious deaths were being linked to the Beasts.

Controversial lyrics

The case has profoundly shocked Italy, still a very Catholic country.

One priest, Don Aldo Buonaito, has set up a helpline for parents and children worried about satanism.

A spate of church burnings in Norway were linked to black metal

He has also called for death metal music to be banned.

"If music makes itself an instrument of nefarious deeds and death it should be stopped," he says.

But this is just the latest case where extreme metal music has been blamed for vicious acts by teenagers.

Everyone remembers the secret messages that were supposed to be contained in Ozzy Osbourne's lyrics and the controversy over his track Suicide Solution.

In 1996, the parents of Elyse Marie Pahler took satanic death metal band Slayer to court in the US after their 15-year-old daughter was murdered in what was alleged to be a satanic ritual imitating the band's lyrics.

The case was dismissed by a Californian judge in 2001.

In Norway fans of the even more extreme black metal, burned down more than 40 churches in the 1990s.

One of the favourite bands of the Beasts of Satan sect in Italy was Deicide - an American death metal band led by Glen Benton, a self-professed satanist who has an upside down cross branded into his forehead.

Lack of evidence

Glen Benton has an upside down cross branded into his forehead

Deicide sing about the occult, their most popular anthem being Kill the Christians.

Other death metal bands appear to glorify murder, torture, rape and necrophilia.

Benton is no stranger to controversy - several murders have been linked to his fans - but denies that any singer can be responsible for the actions of their fans.

"I say don't blame people like me and [Marilyn] Manson, because we never said: 'Hey, we're going to be role models for all your kids.' That ain't what this is about. It's about entertainment."

Indeed there is little evidence that ordinary kids can be turned into monsters by music.

But academics who have studied adolescents and music have expressed concerns about the possible effects on children who already have psychological problems.

Professor Don Roberts of Stanford University thinks that perhaps the children who are already violent or depressed are the people who should be kept away from death metal.

"What the music may well be doing is simply reinforcing beliefs that they might have started with in the first place," he says.

Death Metal Murders was broadcast on Thursday, 24 November, 2005 at 2100 GMT on BBC Two.